1. Field of the Invention
Embodiments described herein relate generally to a magnetic resonance imaging apparatus and a guiding method of coil selection in magnetic resonance imaging method.
2. Description of the Related Art
MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) placed in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation. The aforementioned MRI means magnetic resonance imaging, the RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal.
Here, an RF (Radio Frequency) coil device is a device which transmits an RF pulse to nuclear spin inside an object by, for example, supplying a coil with an RF pulse electric current and detects generated echo signals as MR signals. RF coil devices can be classified into a whole body type and a local area type. Various types of the RF coil devices for a local area are used according to an imaging part. For example, in the case of imaging of lower limbs, a dedicated RF coil device for lower limbs is loaded to the lower limbs of an object.
Inside wearable type of RF coil devices, for example, a plurality of coil elements that function as antennas for detecting MR signals are disposed. In the preparation phase of imaging, for example, (each group of) the respective coil elements inside an RF coil device are displayed, and (the groups of) the coil elements used for imaging are selected by a user. As to selection of the coil elements used for imaging, the respective positions of the coil elements are important.
Then, in Patent Document 1, a reception intensity distribution of each coil element to MR signals in the Z axis direction is obtained in order to accurately calculate the respective positions of the coil elements, and a representative position of the RF coil device is calculated on the basis of the peak position of the reception intensity distribution.
[Patent Document 1] Japanese Patent Application Laid-open (KOKAI) Publication No. 2010-259777
In Patent Document 1, the respective positions of the plurality of coil elements are displayed on the basis of the representative position.
Although the invention of Patent Document 1 can calculate the representative position and the position of each coil element with satisfactorily high degree of precision, it is preferable to detect the representative position and the position of each coil element as accurately as possible. For example, the coil elements that are too distant from the magnetic center are considered to have insufficient reception sensitivity for obtaining sufficient image quality, and it is preferable to exclude such coil elements from the coil elements selected for imaging.
Thus, a novel technology to judge (determine) coil elements which are effective for imaging in MRI has been desired, and as one of methods for achieving that, a novel technology to detect position of an RF coil device in MRI more accurately than the conventional technology has been desired.